1. Field of the Invention
The present invention relates to beam forming acoustic arrays and, more particularly, to broad band, high frequency, high sensitivity beam forming acoustic arrays operable at high hydrostatic pressure.
2. Description of the Related Art
A conventional sonar system typically utilizes a broad band, high frequency, high sensitivity beam forming array as an antenna. The specific array design is dependent on the particular array application. For example, the array design can be varied to meet specific free-field voltage sensitivity requirements and hydrostatic pressure requirements while being operable over a defined frequency range.
Conventional acoustic arrays having multiple sensor elements use a piezoelectric material such as lead zirconate-lead titanate (PZT) which requires a pressure release material to surround and back each of the sensor elements of the array. Although this type of array design will met all acoustic design constraints, such arrays fail to met the hydrostatic restraints because of the pressure release material. The use of the array in high pressure environments causes the pressure element to be compressed. As a result, the pressure release material expands and presses against the sensor elements causing an acoustic coupling that deteriorates the array performance.
Therefore, conventional arrays do not meet the more demanding underwater performance parameters. For example, conventional arrays are not able to operate from 10 kHz to above 100 kHz, while having a free-field voltage sensitivity (FFVS) of -186 dB re 1V/.mu.Pa or greater wherein the FFVS does not change more than plus or minus 2 dB at hydrostatic pressures varying from 20 to 4481.6 kPa (3 to 650 psi).